1. Field of the Invention
The present invention relates to an automatic focus adjustment technique in an image capture apparatus.
2. Description of the Related Art
A focus detection apparatus which detects relative movement of a main object, to undergo focus detection, on a two-dimensional image sensing plane based on a change in luminance signal or color difference signal, thereby moving the focus detection position in accordance with the movement of the main object has conventionally been proposed, as described in Japanese Patent Laid-Open No. 60-249477.
A focus detection apparatus which predicts the focus position of a main object a predetermined time into the future based on a temporal change in characteristic of focus detection while continuously performing focus detection of the main object has conventionally been proposed as well, as described in Japanese Patent No. 03218730.
The focus detection apparatus described in Japanese Patent No. 03218730 calculates a moving velocity change curve in the direction in which the main object moves on the image plane based on the focus detection result obtained within a predetermined elapsed time to predict the focus position of the main object a predetermined time into the future. Before a moving velocity change curve is calculated, it is determined whether the change in velocity at which the main object moves on the image plane exceeds a predetermined threshold. If the change in velocity at which the main object moves on the image plane is small, a moving velocity change curve in the direction in which the main object moves on the image plane is calculated based on the focus detection result obtained over a relatively long elapsed time. If the change in velocity at which the main object moves on the image plane is great then a moving velocity change curve is calculated based on the focus detection result over a relatively short elapsed time. With such an operation, the prediction error can be kept small to a certain degree.
A focus detection apparatus which can perform focus detection of a main object even if the main object moves rapidly has been proposed, as described above. However, when focus detection is performed for, for example, a figure skater, the direction in which he or she moves may change rapidly in the middle of the performance due, for example, to a jump or fall, so it is difficult to continue to focus on the skater. This is because not only the velocity of the main object in the direction in which the main object moves on the image plane but also the composition of the main object on the two-dimensional image sensing plane changes.